Certain early papers have lasted for over a thousand years and many papers made during the Middle Ages are still in excellent condition. Such paper made in the Middle Ages is still good and is expected to last for centuries, but modern paper becomes brittle and disintegrates within 5 to 75 years. The investigations of Barrow as reported in Permanence/Durability of the Book, Barrow Research Laboratories, Richmond, Va., 1963, and others have established that acid paper has a short life whereas paper which has a pH of 7 or slightly above will remain supple and not appear to age by discoloration.
Paper has been made on the acid side since the early years of the 19th century when the use of rosin/alum sizing was introduced. Even today, the major portion of the paper produced is of this acid sized paper. Libraries, therefore, are filled with books in which the paper is degrading at a rather rapid rate into a brittle, yellow dust. The Library of Congress itself has an estimated 6 million books which are already in such condition that they should not circulate and with minor exceptions the whole collection of the Library of Congress should be neutralized and buffered to halt degradation. For the Library of Congress alone, that would be 3,000 tons of books that require emergency treatment. The Library of Congress is not alone, and this same condition exists in almost every library of the United States and most foreign countries where the paper is manufactured with an acid sizing treatment. This phenomenum is easily observed in the Patent Office itself by viewing the degradation of the patents within the shoes. As one conducts a search, one finds that the patents become yellow and brittle as one proceeds back in date order to patents that are 25 years old and older.
Many methods have been devised for neutralizing the acid nature of paper, but most of these entail an individual or small batch treatment of paper in various solvents. Such prior methods and an improved small batch method itself are discussed in our co-pending application, Ser. No. 447,120 entitled "IMPROVED METHOD OF DEACIDIFYING PAPER" filed Feb. 28, 1974, now U.S. Pat. No. 3,898,356. These first methods, such as the one suggested by Barrow and discussed in our co-pending application, utilized various methods of dipping or spraying the buffering agent onto the paper. Such solvent and aqueous treatments are not adaptable to a mass method and may often leave a book warped and the paper cockled. With solvent based treatments, one must carefully test the materials to avoid destroying or damaging the inks and color values of prints contained within the books. All of these methods, both aqueous and solvent methods, can often be damaging to leather, plastic, or other binding materials as are commonly used to produce and bind modern books.
Some methods for the use of a volatile buffering or neutralizing agent have previously been suggested. Several volatile phosphorous compounds which are alkaline have been suggested, although these compounds are extremely toxic and would not be primarily useful in such a process unless the toxicity imparted to the paper impregnated with such material could be controlled or would not be a problem. Various persons have experimented with variations of the volatile/alkaline/nitrogen compounds such as ammonia and its related amines. Work on neutralization and buffering, using a vapor, has been reported by Langwell in U.S. Pat. No. 3,472,611, issued Oct. 14, 1969. In the Langwell method, an impregnated sheet or powder is interleaved between the pages of a book to be preserved and said book is stored for a period time to allow the penetration of the pages with the base material. The material itself is described as a non-deliquescent salt of a reaction product of a normally liquid mono-amine and an acid. The salts are usually acetates and carbonates of cyclohexylamine, diisopropylamine, piperdine, morpholine, or various butylamines. The method described by Langwell, of course, suffers from the problem that the amine will have a tendency to dissipate from the neutralized book over a period of time, allowing the natural acid conditions of the book and the atmosphere to return.
Kusterer, in U.S. Pat. No. 3,703,353, issued Nov. 21, 1972, described an impregnation of paper with hexamethylenetetramine wherein the hexamethylenetetramine is produced by reacting ammonia and formaldehyde in gaseous form to impregnate the paper. Kusterer, et al., in U.S. Pat. No. 3,771,958, issued Nov. 13, 1973, discloses a method of impregnating and neutralizing paper by exposing it to gaseous morpholine.
Another vapor method of treating paper is shown by Smith in U.S. Pat. No. 3,676,055, issued July 11, 1972. Smith does not neutralize the paper itself in a vapor method, but instead uses an alcoholic solution of magnesium methoxide to neutralize the paper and then introduces ethylene oxide, which is a well knwon fumigant agent, to fumigate the books against vermin and to improve the aging characterstics of the treated paper.
The Langwell paper deacidification has been discusssed by Dupuis, et al. in Restaurator, Volume I, No. 3, pp. 149-164, of 1970. The use of such compounds as the cyclohexylamine and morpholine suffer from the problem that the compounds themselves have an unpleasant odor and have a tendency to exude from the treated volumes over the course of time until they are totally dissipated. The various amines leave an unpleasant odor which is detrimental to their use.